The disclosure introduces a new concept in commercially practicable ditching machines; that of the manually portable and manually propelled endless chain trencher.
The problems addressed in the actual commercial production of a truly portable trencher derive from limitations that are not present in conventional trenchers. The most obvious is weight which, in turn, is a function of that power plant limitation that has previously defeated the trenching depth and speed requirements of a commercially acceptable, portable ditcher. Thus, the design considerations which allow considerable latitude in the choice of an endless chain digger tooth configuration adapted for recirculation by a power plant of virtually unlimited horsepower and/or adapted for powered propulsion through the earth are quite different from one adapted for manual transport and manual propulsion through the earth. The difference is one of tooth element configuration conforming to power plant capacity as opposed to selection of a desired horsepower rating to recirculate a desired tooth configuration.
The distinction is simply stated but is fully explanatory of the reason why the portable ditcher herein disclosed, which is in commercial use in virtually every major country in the world, has had no commercial predecessor.
The expression "portable ditcher" as used herein refers to that size and weight ditcher that can be both manually carried for transport and manually propelled through the earth during a trenching operation. As will be apparent, an overall unit weight exceeding much over fifty pounds would not be consistent with this truly portable aspect for ready transport and extended trenching operations by the average person.
Considering the weight constraints of the overall unit including the gear box and cutter bar the size power plant that can be employed translates to a power rating in the range of 3-31/2 horsepower. Typical trenching depths for various pipe and cable laying operations vary from 6 to 18 inches with some depth requirements approaching two feet. With sufficient power plant capacity there is, of course, no difficulty in digging a relatively narrow trench, as on the order of 2-3 inches, to these depths. The problem arises when the task is sought to be accomplished, at commercially acceptable speeds, with a small power source such as a 3 horsepower chain saw motor, for example.
The key to the successful employment of small power sources of the type described for trenching at eminently acceptable commercial speeds of 10-20 feet per minute, depending upon soil conditions, is drag reduction; primary emphasis is on tooth drag and secondary emphasis on chain drag.
Prior art attempts to produce relatively small ditchers have, for the most part, employed chain and tooth configurations quite suitable for recirculation by a large power source but have made little if any concessions to such design as would enable the same to function effectively with small power plants of the type herein contemplated. Exemplary are the disclosures in U.S. Pat. Nos. 2,991,571 and 3,054,198.
In general, dynamic tooth drag, per se, varies inter alia, with:
(1) tooth size,
(2) lateral working angle of attack,
(3) trailing surface area configuration in earth contact, and
(4) tooth tracking alignment
while chain drag is primarily a function of lateral force components, imparted by the teeth, tending to offset the chain from a straight run as well as actual chain engagement with an uncut central seam and, secondarily, of frictional contact with the cutter bar and excessive tensioning due to sprocket fouling.
A partial solution to the problem of excessive tooth drag to the extent of employing relatively small teeth having a small lateral angle of attack appears in U.S. Pat. No. 3,614,838 which is assigned to the owner of the present invention in the actual use of which, however, unacceptably high drag forces are imposed by the trailing surface area configurations of the teeth.
Until the introduction of the present ditcher, the weight of the smallest, narrow trenching equipment commercially available for pipe and cable laying has been measured in hundreds of pounds the weight of which not only requires trailerable transport but insures the potential for surface damage in certain trenching environments such as, for example, wheel track indentations in residential lawns during sprinkler system installation. In contrast, since the present ditcher weighs well under fifty pounds it is equally adaptable for hand-held use or mounting to a small hand-propelled dolly allowing the operator to remain upright during trenching operations.
Another feature of the invention is the ready convertability of the ditcher from a hand-held use mode to a dolly-supported condition requiring nothing more than a two bolt assembly for stable securement.
With the power source necessarily adjacent the exhaust end of the chain run the otherwise short working life of the intake filter is substantially extended, in the dolly-mounted mode, by the use of a second, series connected filter positioned upstream of the engine mounted filter and supported at a location remote from the chain run.